How to manage responses from Plugin

Hello,

So I have progressed pretty far to get my plugin where I want it to be. I have a problem though.

SO I call a simple GET
When using in the browser:

$this->plugin->setResponse("Created a New SubScription");

seems to work fine. I see a blank screen with "Created a New SubScription" written out.

However whenever I call this from curl and save the response I get all the HTML surrounding "Created a New SubScription". is there anyway to stop this?

Ideally I would like to send back a JSON / Swagger File of the resource they wish to View.

Thanks.